We present a semi-analytic, physically motivated model for dark matter halo concentration as a function of halo mass and redshift. The semi-analytic model combines an analytic model for the halo mass ...accretion history (MAH), based on extended Press–Schechter (EPS) theory, with an empirical relation between concentration and formation time obtained through fits to the results of numerical simulations. Because the semi-analytic model is based on EPS theory, it can be applied to wide ranges in mass, redshift and cosmology. The resulting concentration–mass (c–M) relations are found to agree with the simulations, and because the model applies only to relaxed haloes, they do not exhibit the upturn at high masses or high redshifts found by some recent works. We predict a change of slope in the z ∼ 0 c–M relation at a mass-scale of 1011 M⊙. We find that this is due to the change in the functional form of the halo MAH, which goes from being dominated by an exponential (for high-mass haloes) to a power law (for low-mass haloes). During the latter phase, the core radius remains approximately constant, and the concentration grows due to the drop of the background density. We also analyse how the c–M relation predicted by this work affects the power produced by dark matter annihilation, finding that at z = 0 the power is two orders of magnitude lower than that obtained from extrapolating best-fitting c–M relations. We provide fits to the c–M relations as well as numerical routines to compute concentrations and MAHs.
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Understanding the universal accretion history of dark matter haloes is the first step towards determining the origin of their structure. We use the extended Press–Schechter formalism to derive the ...halo mass accretion history from the growth rate of initial density perturbations. We show that the halo mass history is well described by an exponential function of redshift in the high-redshift regime. However, in the low-redshift regime the mass history follows a power law because the growth of density perturbations is halted in the dark energy dominated era due to the accelerated expansion of the Universe. We provide an analytic model that follows the expression
${M(z)=M_{0}(1+z)^{af(M_{0})}{\rm e}^{-f(M_{0})z}}$
, where M
0 = M(z = 0), a depends on cosmology and f(M
0) depends only on the linear matter power spectrum. The analytic model does not rely on calibration against numerical simulations and is suitable for any cosmology. We compare our model with the latest empirical models for the mass accretion history in the literature and find very good agreement. We provide numerical routines for the model online (available at https://bitbucket.org/astroduff/commah).
Measurement of the spatial distribution of neutral hydrogen via the redshifted 21-cm line promises to revolutionize our knowledge of the epoch of reionization and the first galaxies, and may provide ...a powerful new tool for observational cosmology from redshifts 1<z<4. In this review we discuss recent advances in our theoretical understanding of the epoch of reionization (EoR), the application of 21-cm tomography to cosmology and measurements of the dark energy equation of state after reionization, and the instrumentation and observational techniques shared by 21-cm EoR and postreionization cosmology machines. We place particular emphasis on the expected signal and observational capabilities of first generation 21-cm fluctuation instruments.
We explore the relation between the structure and mass accretion histories of dark matter haloes using a suite of cosmological simulations. We confirm that the formation time, defined as the time ...when the virial mass of the main progenitor equals the mass enclosed within the scale radius, correlates strongly with concentration. We provide a semi-analytic model for halo mass history that combines analytic relations with fits to simulations. This model has the functional form, M(z) = M
0(1 + z)α
e
βz
, where the parameters α and β are directly correlated with concentration. We then combine this model for the halo mass history with the analytic relations between α, β and the linear power spectrum derived by Correa et al. to establish the physical link between halo concentration and the initial density perturbation field. Finally, we provide fitting formulae for the halo mass history as well as numerical routines. We derive the accretion rate as a function of halo mass, and demonstrate how the halo mass history depends on cosmology and the adopted definition of halo mass.
ABSTRACT
We examine the properties of the host galaxies of $z=7$ quasars using the large volume, cosmological hydrodynamical simulation BlueTides. We find that the 10 most massive black holes and the ...191 quasars in the simulation (with $M_{\textrm{UV,AGN}}\lt M_{\textrm{UV,host}}$) are hosted by massive galaxies with stellar masses $\log (M_\ast /\, {\rm M}_{\odot })=10.8\pm 0.2$, and $10.2\pm 0.4$, which have large star formation rates of $513_{-351}^{+1225}\, {\rm M}_{\odot }/\rm {yr}$ and $191_{-120}^{+288}\, {\rm M}_{\odot }/\rm {yr}$, respectively. The hosts of the most massive black holes and quasars in BlueTides are generally bulge-dominated, with bulge-to-total mass ratio $B/T\simeq 0.85\pm 0.1$; however, their morphologies are not biased relative to the overall $z=7$ galaxy sample. We find that the hosts of the most massive black holes and quasars are compact, with half-mass radii $R_{0.5}=0.41_{-0.14}^{+0.18}$ kpc and $0.40_{-0.09}^{+0.11}$ kpc, respectively; galaxies with similar masses and luminosities have a wider range of sizes with a larger median value, $R_{0.5}=0.71_{-0.25}^{+0.28}$ kpc. We make mock James Webb Space Telescope (JWST) images of these quasars and their host galaxies. We find that distinguishing the host from the quasar emission will be possible but still challenging with JWST, due to the small sizes of quasar hosts. We find that quasar samples are biased tracers of the intrinsic black hole–stellar mass relation, following a relation that is 0.2 dex higher than that of the full galaxy sample. Finally, we find that the most massive black holes and quasars are more likely to be found in denser environments than the typical $M_{\textrm{BH}}\gt 10^{6.5}\, {\rm M}_{\odot }$ black hole, indicating that minor mergers play at least some role in growing black holes in the early Universe.
We introduce meraxes, a new, purpose-built semi-analytic galaxy formation model designed for studying galaxy growth during reionization. meraxes is the first model of its type to include a temporally ...and spatially coupled treatment of reionization and is built upon a custom (100 Mpc)3
N-body simulation with high temporal and mass resolution, allowing us to resolve the galaxy and star formation physics relevant to early galaxy formation. Our fiducial model with supernova feedback reproduces the observed optical depth to electron scattering and evolution of the galaxy stellar mass function between z = 5 and 7, predicting that a broad range of halo masses contribute to reionization. Using a constant escape fraction and global recombination rate, our model is unable to simultaneously match the observed ionizing emissivity at z ≲ 6. However, the use of an evolving escape fraction of 0.05–0.1 at z ∼ 6, increasing towards higher redshift, is able to satisfy these three constraints. We also demonstrate that photoionization suppression of low-mass galaxy formation during reionization has only a small effect on the ionization history of the intergalactic medium. This lack of ‘self-regulation’ arises due to the already efficient quenching of star formation by supernova feedback. It is only in models with gas supply-limited star formation that reionization feedback is effective at regulating galaxy growth. We similarly find that reionization has only a small effect on the stellar mass function, with no observationally detectable imprint at M
* > 107.5 M⊙. However, patchy reionization has significant effects on individual galaxy masses, with variations of factors of 2–3 at z = 5 that correlate with environment.
The earliest generation of stars and black holes must have established an early 'Lyman-Werner' background (LWB) at high redshift, prior to the epoch of reionization. Because of the long mean free ...path of photons with energies hν < 13.6 eV, the LWB was nearly uniform. However, some variation in the LWB is expected due to the discrete nature of the sources, and their highly clustered spatial distribution. In this paper, we compute the probability distribution function (PDF) of the LW flux that irradiates dark matter (DM) haloes collapsing at high redshift (z≈ 10). Our model accounts for (i) the clustering of DM haloes, (ii) Poisson fluctuations in the number of corresponding star-forming galaxies and (iii) scatter in the LW luminosity produced by haloes of a given mass (calibrated using local observations). We find that >99 per cent of the DM haloes are illuminated by an LW flux within a factor of 2 of the global mean value. However, a small fraction, ∼10−8 to 10−6, of DM haloes with virial temperatures T
vir≳ 104 K have a close luminous neighbour within ≲10 kpc, and are exposed to an LW flux exceeding the global mean by a factor of >20, or to J
21,LW > 103 (in units of 10−21 erg s−1 Hz−1 sr−1 cm−2). This large LW flux can photodissociate H2 molecules in the gas collapsing due to atomic cooling in these haloes, and prevent its further cooling and fragmentation. Such close halo pairs therefore provide possible sites in which primordial gas clouds collapse directly into massive black holes (M
BH≈ 104−6M⊙), and subsequently grow into supermassive (M
BH≳ 109M⊙) black holes by z≈ 6.
We study the visibility of the Lyα emission line during the epoch of reionization. Combining galactic outflow models with large-scale seminumeric simulations of reionization, we quantify the ...probability distribution function of the fraction of Lyα photons transmitted through the intergalactic medium (IGM),
. Our study focuses on galaxies populating dark matter haloes with masses of M
halo= 1010 M⊙ at z= 8.6, which is inspired by the recent reported discovery of a galaxy at z= 8.6 with strong Lyα line emission. For reasonable assumptions, we find that the combination of winds and reionization morphology results in
per cent (50 per cent), for the majority of galaxies, even when the Universe is ∼80 per cent (60 per cent) neutral by volume. Thus, the observed strong Lyα emission from the reported z= 8.6 galaxy is consistent with a highly neutral IGM, and cannot be used to place statistically significant constraints on the volume-averaged neutral fraction of hydrogen in the IGM. We also investigate the implications of the recent tentative evidence for an observed decrease in the 'Lyman alpha emitter fraction' among drop-out galaxies between z= 6 and 7. If confirmed, we show that a rapid evolution in
will be required to explain this observation via the effects of reionization.
We summarize panchromatic Extragalactic Background Light data to place upper limits on the integrated near-infrared surface brightness (SB) that may come from Population III stars and possible ...accretion disks around their stellar-mass black holes (BHs) in the epoch of First Light, broadly taken from z 7-17. Theoretical predictions and recent near-infrared power spectra provide tighter constraints on their sky signal. We outline the physical properties of zero-metallicity Population III stars from MESA stellar evolution models through helium depletion and of BH accretion disks at . We assume that second-generation non-zero-metallicity stars can form at higher multiplicity, so that BH accretion disks may be fed by Roche-lobe overflow from lower-mass companions. We use these near-infrared SB constraints to calculate the number of caustic transits behind lensing clusters that the James Webb Space Telescope and the next-generation ground-based telescopes may observe for both Population III stars and their BH accretion disks. Typical caustic magnifications can be , with rise times of hours and decline times of year for cluster transverse velocities of km s−1. Microlensing by intracluster-medium objects can modify transit magnifications but lengthen visibility times. Depending on BH masses, accretion-disk radii, and feeding efficiencies, stellar-mass BH accretion-disk caustic transits could outnumber those from Population III stars. To observe Population III caustic transits directly may require monitoring 3-30 lensing clusters to mag over a decade.
Low-frequency observatories are currently being constructed with the goal of detecting redshifted 21-cm emission from the epoch of reionization. These observatories will also be able to detect ...intensity fluctuations in the cumulative 21-cm emission after reionization, from hydrogen in unresolved damped Lyα absorbers (such as gas-rich galaxies) down to a redshift z∼ 3.5. The inferred power spectrum of 21-cm fluctuations at all redshifts will show acoustic oscillations, whose comoving scale can be used as a standard ruler to infer the evolution of the equation of state for the dark energy. We find that the first generation of low-frequency experiments (such as MWA or LOFAR) will be able to constrain the acoustic scale to within a few per cent in a redshift window just prior to the end of the reionization era, provided that foregrounds can be removed over frequency bandpasses of ≳8 MHz. This sensitivity to the acoustic scale is comparable to the best current measurements from galaxy redshift surveys, but at much higher redshifts. Future extensions of the first-generation experiments (involving an order of magnitude increase in the antennae number of the MWA) could reach sensitivities below 1 per cent in several redshift windows and could be used to study the dark energy in the unexplored redshift regime of 3.5 ≲z≲ 12. Moreover, new experiments with antennae designed to operate at higher frequencies would allow precision measurements (≲1 per cent) of the acoustic peak to be made at more moderate redshifts (1.5 ≲z≲ 3.5), where they would be competitive with ambitious spectroscopic galaxy surveys covering more than 1000 deg2. Together with other data sets, observations of 21-cm fluctuations will allow full coverage of the acoustic scale from the present time out to z∼ 12.
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